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Hansen, A. P., Pate, J. S. and Atkins, C. A. 1987. Relationshipsbetween acetylene reduction activity, hydrogen evolution andnitrogen fixation in nodules of Acacia spp.: Experimental backgroundto assaying fixation by acetylene reduction under field conditions.J.exp. Bot. 38: 112 Glasshouse grown, symbiotically-dependent seedlings of Acaciaalata R.Br., .A. extensa Lindl., and A. pulchella R.Br. wereexamined for acetylene reduction in closed assay systems usingundisturbed potted plants, excavated whole plants, nodulatedroots or detached nodules. Nitrogenase activity declined sharplyover the first hour after exposure of detached nodules to acetylene(10% v/v in air), less steeply or not at all over a 3 h periodin assays involving attached nodules. Using detached nodules,rates of acetylene reduction, nitrogen (15N2) fixation, andhydrogen evolution in air (15N2) and acetylene-containing atmosphereswere measured in comparable 30 min assays. Total electron flowthrough nitrogenase in air was determined from rates of nitrogen(15N2) fixation ( ? 3) plus hydrogen evolution, that in thepresence of acetylene from rates of acetylene reduction andhydrogen evolution in air: acetylene. Values for the ratio ofelectron flow in air: acetylene to that in air ranged from 0?43to 0?83 in A. pulcheila, from 0?44 to 0?66 in A. alala and from0?37 to 0?70 in A. extensa, indicating substantial inhibitionof electron flow through nitrogenase of detached nodules byacetylene. Relative efficiencies of nitrogenase functioningbased on hydrogen evolution and acetylene reduction were from0?15 to 0?79, those based on nitrogen (15N2) fixation and hydrogenevolution from 0?53 to 0?87. Molar ratios of acetylene reducedto nitrogen (15N2) fixed were 2?82 ? 0?24, 201 ? 0?15, and 1?91? 0?11 (?s.e.; n = 7) for A. pulcheila,A. extensa and A. alata respectively A standard 510 min acetylene reduction assay, conductedon freshly detached unwashed nodules in daytime (12.0014.00h), was calibrated for field use by comparing total N accumulationof seedlings with estimated cumulative acetylene reduction overa 7-week period of glasshouse culture. Molar ratios for acetylenereduced: nitrogen fixed using this arbitrary method were 3?58for A. alata, 4?82 for A. extensa and 1?60 for A. pulchella.The significance of the data is discussed. Key words: Acacia spp, nitrogenase functioning 相似文献
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To investigate factors affecting the ability of introduced species to invade natural communities in the Western Australian wheatbelt, five communities were examined within a nature reserve near Kellerberrin. Transect studies indicated that introduced annuals were more abundant in woodland than in shrub communities, despite an input of introduced seed into all communities. The response of native and introduced annuals to soil disturbance and fertilizer addition was examined. Small areas were disturbed and/or provided with fertilizer prior to addition of seed of introduced annuals. In most communities, the introduced species used (Avena fatua and Ursinia anthemoides) established well only where the soil had been disturbed, but their growth was increased greatly when fertilizer was also added. Establishment and growth of other introduced species also increased where nutrient addition and soil disturbance were combined. Growth of several native annuals increased greatly with fertilizer addition, but showed little response to disturbance. Fertilizer addition also significantly increased the number of native species present in most communities. This indicates that growth of both native and introduced species is limited by nutrient availability in these communities, but also that introduced species respond more to a combination of nutrient addition and soil disturbance. 相似文献
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Diurnal Patterns of Transport and Accumulation of Minerals in Fruiting Plants of Lupinus angustifolius L. 总被引:2,自引:0,他引:2
Fluctuations in mineral elements id xylem (tracheal) sap, fruitphloem sap, leaflets and dmloping fruits were studied in a fieldpopulation of Lupinus angustifolius L. by three-hourly samplingover a 39 h period. Elements usually reached maximum contentsor concentrations at or near noon, minimum levels during thenight. Amplitudes of diurnal fluctuations in minerals lay withinthe range ±433 per cent of the mean content ofleaflets, and ±17157 per cent of the mean concentrationsin xylem and phloem sap. Most minerals elements fluctuatcd inphase with daily changes in sugar level of phloem sap and drymatter and carbohydrate fluctuations of leaflets, suggestinga coupling of translocation of photosynthate and minerals fromthe leaflets. Rates of import of minerals by shoots wereestimatedfrom shoot transpiration and mineral concentrations in trachealsap. Average day time rates of import of most elements were1225 times those at night. Translocation of minerals,nitrogen and carbon to fruits also exhibited diurnal periodicity,average rates of import king three to seven times higher inthe day than at night. A model of transport based on the carbonand water economy of the fruit suggested that P, K, Fe, Zn,Mn and Cu were imported predominantly by phloem. Estimates ofvascular import accounted for 87104 per cent of the fruit'sactual increment of these elements. Na and Ca were gauged tobe imported mainly by xylem, Mg almost equally by xylem andphloem. However, large discrepancies existed for these threeelements between estimated vascular import and actual intakeby the fruit. Lupinus angustifolius L., mineral transport, accumulation, fruits, xylem sap, phloem sap, transpiration 相似文献
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Nitrogen metabolism and transport were studied during reproductivedevelopment of cowpea (Vigna unguiculata (L.) Walp. cv. Vita3) under three contrasting nitrogen regimes: (1) nitrate suppliedcontinuously (plants non-nodulated), (2) symbiotic N2 fixation(no combined nitrogen), (3) nitrogenstarvation post-anthesisof previously N2-fixing plants. The last treatment involveddaily flushing of the root systems with 100% oxygen which suppressedpost-anthesis N2-fixation by 7679%, thereby making fruitgrowth almost entirely reliant upon mobilization of previouslyaccumulated nitrogen. The bulk of the xylem nitrogen (root bleedingsap or peduncle tracheal sap) of nitrate-fed plants was nitrateand amide, that of symbiotic and O2-treated plants largely ureide.The composition of fruit cryopuncture phloem sap, however, wasclosely similar in all treatments, with most nitrogen as amidesand amino acids. The evidence suggested intense metabolic transferof root derived nitrate-N or ureide-N to amino acids by vegetativeplant parts prior to translocation to fruits. All tissues offruits showed patterns of development of enzymic activitiesconsistent with release of nitrogen from both ureides and amidesand re-assimilation of ammonia to form amino acids. Althoughthe levels of enzyme activities varied between treatments thedifferences could not be readily associated with individualpatterns of nitrogen transport in the treatments. Nitrogen sufficiencyin the NO3-fed plants was marked by elevated vegetative biomassand low harvest indices for dry matter and nitrogen, while nitrogendeficiency of the O2-treated plants was associated with seedabortion, small seed size and low seed nitrogen concentration,and efficient mobilization of nitrogen from vegetative partsto fruits. Key words: Nitrogen, Translocation, Cowpea 相似文献
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Patterns of flow of nitrogen were constructed for the post-anthesisdevelopment of symbiotically-dependent cowpea (Vigna unguiculataWalp. cv. Vita 3-Rhizobium CB756). Nitrogen fixed after floweringcontributed 40% of the fruits' total intake of N, mobilizationof N fixed before flowering the remaining 60%. Leaflets, nodulatedroot, stem plus petioles, and peduncles contributed mobilizedN in the approximate proportions 5: 2: 1: 1 respectively. Eachfruit drew on all available current sources of N, but N fromleaves was distributed preferentially to closest fruit(s), andlower fruits monopolized the N exported from nodulated rootsduring late fruiting. Rates of nitrogen fixation declined parallel with decreasingnet photosynthesis of shoots. Leaflets at upper reproductivenodes mobilized 7077% of their N and declined steeplyin net photosynthesis rate per unit chlorophyll or per unitribulose-l, 5-bisphosphate carboxylase (RuBPCase)2 before abscisingduring mid- to late fruiting, whereas leaflets at lower vegetativenodes (13) mostly failed to abscise, lost 4457%of their N and maintained photosynthetic activity throughoutfruiting. Peptide hydrolase activity was examined in extracts of leaflets,roots and nodules, by autodigestion of extracts, or in assaysusing bovine haemoglobin and purified RuBPCase isolated fromcowpea as substrates. Hydrolase activities during fruiting werebroadly related to N loss from plant organs, but asynchronyin peaks of activity against different protein substrates indicateddistinct groups of hydrolases within single organs. Hydrolaseactivity of leaflet extracts against RuBPCase was highly andpositively correlated with in vivo rates of loss of RuBPCasefrom the same leaflets, and preferential degradation of thisprotein occurred during leaflet senescence. Key words: Nitrogen, Mobilization: Cowpea 相似文献
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Seedlings (180-d-old) of Casuarina cunninghamianaM L., C. equisetifoliaMiq. and C. glauca Sieber inoculated with each of two differentsources of Frankia, were analysed for translocated nitrogenouscompounds in xylem sap. Analyses were also made on sap fromnodulated and non-nodulated plants of C. glauca grown with orwithout a range of levels of combined nitrogen. Xylem exudateswere collected from stems, roots, and individual nodules ofnodulated plants and from stems and roots of non-nodulated plants.While the proportional composition of solutes varied, the samerange of amino compounds was found in xylem sap from the threedifferent symbioses. In C. glauca asparagine was the major aminoacid in the root sap followed by proline, while in symbioticC. cunninghamiana arginine accounted for more than 25% of theamino compounds. Citrulline was the major translocated productfound in the stem exudate of symbiotic C. equisetifolia. Increasingconcentrations of ammonium nitrate in the nutrient solutionresulted in increasing levels of free ammonia and glutaminein xylem sap from stems of nodulated and non-nodulated C. glauca,but there was relatively little change in the prominent solutes,e.g. citrulline, proline, and arginine. The composition of nitrogenoussolutes in stem or root exudates of C. glauca was similar tothat of exudate collected from individual nodules and on thisbasis it was not possible to distinguish specific products ofcurrent N2 fixation in xylem. The main differences in N solutecomposition between the symbioses were apparently due to hostplant effects rather than nodulation or the levels of combinedN. Also, the data indicate that the use of the proportion ofN in sap as citrulline (or indeed any other organic N solute)could not be used as an index of nitrogen fixation. 相似文献
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Specific Unresponsiveness of Recirculating Lymphocytes after Exposure to Histocompatibility Antigen in F<Subscript>1</Subscript> Hybrid Rats 总被引:25,自引:0,他引:25
SEVERAL investigators have demonstrated the principle of selective removal of a subpopulation of antigen sensitive cells required for a particular antibody response. For example, cells necessary for the antibody response to protein antigens can be specifically removed by passage through an antigen coated column1; cells necessary for the haemolytic plaque forming cell response to sheep erythrocytes can be removed by exposing them to concentrations of 3H-thymidine lethal for DNA synthesizing cells2; and cells necessary for the agglutinin response to flagellin can be removed by treating the population with radioactive flagellin so that the cells which bind the antigen are inactivated3. The cells which remain after these procedures have been shown to have a normal level of activity against non-cross-reacting antigens. These findings are regarded as evidence for heterogeneity in the whole population of antigen sensitive cells such that each cell can only respond to one antigen or to a restricted range of different antigens. 相似文献
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